If the target creature's power is increased to 4 or greater after Gossip's Talent's level 2 class ability triggers but before it resolves, the ability doesn't resolve. However, if instead the creature's power is increased to 4 or greater after the ability resolves, it still can't be blocked that turn.

Gaining a level is a normal activated ability. It uses the stack and can be responded to.

If you choose to exile a creature with double strike when Gossip's Talent's level 3 class ability resolves, it won't be an attacking creature anymore when it returns to the battlefield, and it won't deal combat damage during the regular combat damage step.

Once the exiled permanent returns, it's considered a new object with no relation to the object that it was. Auras attached to the exiled permanent will be put into their owners' graveyards. Equipment attached to the exiled permanent will become unattached and remain on the battlefield. Any counters on the exiled permanent will cease to exist.

Each Class has five abilities. The three in the major sections of its text box are class abilities. Class abilities can be static, activated, or triggered abilities. The other two are level abilities, one activated ability to advance the Class to level 2 and another to advance the Class to level 3.

Each Class starts with only the first of its three class abilities. As the first level ability resolves, the Class becomes level 2 and gains the second class ability. As the second level ability resolves, the Class becomes level 3 and gains the third class ability.

There's no restriction on how many Class permanents you can control, whether they're the same or different classes. Each Class permanent tracks its own level separately.

Gaining a level won't remove abilities that a Class had at a previous level.

Gossip's Talent's level 3 class ability triggers once for each creature you control that deals combat damage to a player during that combat damage step. You choose the order those triggers are put onto the stack. They resolve one at a time; when one resolves, you choose whether or not to exile the appropriate creature.

You can't activate the first level ability of a Class unless that Class is level 1. Similarly, you can't activate the second level ability of a Class unless that Class is level 2.

If a token is exiled this way, it will cease to exist and won't return to the battlefield.